TTY

Stands for teletype, which is a text-over-call feature.

In the U.S., TTY is governed by Title IV of the Americans with Disabilities Act. All telephone companies are required to provide telecommunication relay services by dialing 7-1-1 to reach a telecommunications relay service (TRS), after which an assistant can place a call using the 10-digit number on the caller’s behalf. The caller can then use a TTY to type messages to the party on the other end of the call which will be relayed with the help of a relay assistant.

For more information on the laws governing TTY, see the FCC.